Refining lead



Filed Nov. 1l, 1933 2 Sheets-.Sheet 2 (1f/Jade esi ver/slay Ani/ many Pfocw.: 05s

end

Patented June 9, 1936 UNITED STATES PATENT OFFICE REFINING LEAD George Kenneth Williams, Port Pirie, South Australia, Australia Application November 11, 1933, Serial No. 697,651 In Australia November 25, 1932 14 claims. (o1. '1s-1s) tin, and it is the practice to remove all but a small proportion of theseconstituents in order to produce market lead of a desired degree of purity and to recover the values of these metals.

This removal is usually effected by a series of intermittent refining operations or batch treatments comprisingz- (a) An initial copper drossing operation in which the bulk of the copper and sulphur is removed by liquation;

(b) A softening process in which antimony, arsenic and tin (if present) are oxidized and removed in the form of antimony dross containing a relatively large proportionof leadi (c) A desilverizing process, such as the Parkes process, in which zinc is added whereby silver,

gold and most of the copper'still remaining are removed in the form of zinciferous crusts; and

(d) A zinc refining process in which the zinc content resulting from the desilverizing process and part of thel remaining antimony is oxidized and removed irthe form of zinc dross".

In the following description Antimony dross means the oxidized product obtained from the lead softening treatment and containing the antimony which has been removed from the softened lead.

Antimony slag is a product relatively high in antimony, as compared with antimony dross, which is obtained by subjecting antimony dross to a reducing treatment.

Hard lead means the bullion containing antimony which is obtained by subjecting antimony dross to the aforesaid reducing treatment.

The abovementioned softening and zinc refinlng processes (b) and (d) respectively have heretofore always been carried out by smelters as batch or intermittent treatments in which a charge of bullion is introduced into a. reverberatory furnace or the like and subjected to an oxidizing atmosphere under suitable conditions of temperature whereby the metals. to ,be removed and some of the lead are oxidized and separate in the form of a dross, which iioats on the surface of the bullion and is periodically removed by skimming.

When the grade of the bullion is sufficiently improved by the oxidation oi' the impurities, the bullion is discharged from the furnace and the cycle of operations is repeated with. the succeed` zinc Arefining treatments may be carried out continuously.

The advantages of continuous treatment comprise, increased output from a given furnace, increased metallurgical eillciency, improved control, and lower fuel, labor and maintenance costs.

The improved softening and/or zinc refining processes are particularly advantages as applied to smelter lead when operated in conjunction with a known process for continuous desilverization,

though they may be employed when desilverization is effected by a batch treatment or when lead containing zinc,antimony, arsenic or tin and derived from any source is required to be refined.

It has previously been proposed to continuously soften lead containing antimony by continuously delivering molten lead and molten litharge to a reaction chamber in which they exist as superposed bodies of small dimensions-i. e. as thin layers whereby the litharge removes the .antimony from the lead while softened lead and antimony dross are continuously discharged from separate orifices.

The layers of lead and litharge preferably flow in contrary directions and the antimony content of the lead is progressively reduced from the inlet to the discharge end whilst the antimony content of the litharge is progressively increased.

It was also proposed to produce the molten litharge, required in the process, in an extension of the reaction chamber and through which extension the discharging softened lead was caused to flow.

With this prior process, however, the production of the necessary molten litharge constitutes a separate operation which precedes its employment for the removal of antimony from the inflowing lead.

The present invention briefly comprisescausing molten lead bullion containing one or more readily oxidizable alloying metals (e. g. zinc, antimony, arsenic, tin) to iiow` continuously into a furnace or treating chamber and lead (low in such oxidizable alloying metals) to be discharged continuously therefrom, said bullion, during its passage through the furnace, being subjected to oxidation under suitable conditions of temperature whereby oxides of such oxidizable metal or metals and litharge separate inthe form of liquid slag which exists above the bullion and is continuously or intermittently discharged from the furnace, thereby obviating the separate addition of litharge to the furnace or chamber.

The process is preferably operated so that a relatively thick layer of liquid slag is formed whereby it may be readily separated from the bullion, and the bodies of bullion and slag are preferably, though not necessarily, subjected to such intense agitation (as e. g. by means of jets of air or other suitable gas) as to maintain substantially uniform conditions of temperature and of composition in the bodies of slag and bullion, as opposed to a condition in which the lead is progressively deprived of its oxidizable alloying metals, during its passage through the furnace or chamber. This intense agitation is preferably effected by means of submerged air jets which also directly assist oxidation.

The process may be operated so that, instead of the iniiow and outow of bullion being continuous, either the inflow or outflow or both may be interrupted for short periods which may recur at intervals and the term continuous as employed herein is intended to comprehend such variations of the process as defined above.

An important featureof the invention particularly as applied to the continuous softening of lead, but also applicable to the zinc refining operation, consists in subjecting the bullion, during its passage through the furnace or treating chamber, to such intense agitation that the heat of formation of the oxides produced is sufficient to maintain the required reaction temperature therein Without the use of extraneous heating means, or is suiiicient to reduce the consumption of fuel to a relatively negligible amount as compared with existing practice.

In applying the continuous softening process with intense agitation, it has been found possible to .operate so that a rim or layer of solidied litharge forms on the walls of the furnace adjacent to the metal bath and even on the roof of said furnace,

This rim or layer of litharge forms a protective coating for the furnace walls and roof, and, to some extent, minimizes the loss of heat by conduction.

An important feature of the continuous zinc reining process included in this invention consists in continuously or intermittently supplying to the furnace or treating chamber or to the lead to be treated therein, a suitable reagent which will serve to lower the melting point of the slags formed therein, and, for this purpose, antimony, arsenic, antimony dross (low in copper and silver) from a softening treatment or theI antimony slag or the hard lead produced from antimony dross may be added either continuously or intermittently to the zinc rening furnace or chamber or to th-e lead to be treated therein.

By adding antimony, or one or more of the other said reagents, to the zinc refining furnace, the melting point of the slags produced is lowered an'd they can be readily obtained in the liquid condition, thus enabling the slag to be eiliciently separated in the liquid condition, from the bullion without operating at unduly high temperatures. i

Furthermore, it has been found that such additions of antimony and/or arsenic do not increase the antimony and/or arsenic contents of refined lead produced by this process, but that, on the .other hand, the amount of antimony and/or arsenic in the bullion produced may be smaller than is usually obtained with theordinary batch methods of refining.

Also, the presence of antimony and/or arsenic in the liquid slag of the zinc rening furnace is found to facilitate and expedite the oxidation process.

A further feature of the invention consists of a process for refining argentiferous smelter lead wherein antimony dross (low in silver and copper) obtained from a softening furnace, or antimony slag and/or hard lead produced from Figure 1 is a diagrammatic view in cross sectional elevation of a softening furnace.

Figure 2 is a diagrammatic view in horizontal section of the-furnace shown in Figure 1.

Figure 3 is a flow sheet showing refining procedures in accordance with the invention; and

Figure 4 is a flow sheet showing a modification of the procedure illustrated in Figure 3.

Continuous softening process In the practice of the continuous softening process as applied to the treatment of argentiferous smelter lead, lead bullion, after the copper drossing treatment, may be caused to flow continuously into a reverberatory furnace, whilst softened lead low in antimony and arsenic is continuously discharged from a different portion thereof.

A layerof liquid slag'preferably about two inches in thickness is allowed to accumulate above the surface of the bullion and is then continuously or intermittently discharged through an overflow notch disposed at an appropriate height and serving to maintain the requisite thickness of slag -in the furnace. The softened bullion is discharged through a submerged orice disposed below the slag layer.

The bullion, during its passage through the furnace, is preferably subjected to intense agitation by means of submerged air jets which serve to maintain uniform conditions of temperature in the bath and of composition in the slag and in the bullion respectively, and also to directly assist oxidation of the bullion.

When equilibrium conditions exist between the bodies of bullion and slag, the bullion throughout the furnace, with the exception of a small section adjacent to the inflow thereof, is of low and substantially unvarying grade in the oxidizable impurities (which condition is favorable to oxidation) while the grade of the slag has a definite relation to the grade of the bullion.

Under such circumstances, the rate of flow of the incoming bullion is so related to the temperatu're and oxidation conditions of the furnace that the amount of antimony and arsenic entering the furnace withthe bullion in any interval of time is just suicient to maintain the equilibrium conditions and grade of said bodies of slag and bullion.

Agitation applied in this way exposes the lead and impurities to oxidation at such rate and under such conditions that suicient heat is generated by oxidation of lead and impurities to make it practicable to dispense, if desired, with the whole of the extraneous heating means normally applied to the bath.

In this connection, it has been found that, by

suitably controlling the admission of air to the submerged jets in relation to the size of furnace and the rate of ow of bullion'therethrough, oxidation caused thereby generates sufficient heat to maintain the metal bath at the desired tem-A perature (about 800 C.) without the use of burnf ers or other extraneous heating means, even though the unsoftened bullion owing into the furnace is at a considerably lower temperature than the bath itself.

Furthermore, by eliminating or substantially eliminating extraneous heating means, and by suitably positioning the air jets, it has been found possible to operate the softening process under such conditions that a rim or layer of solidified litharge forms on the Walls of the furnace above the bullion therein and in contact therewith and even on the top of the furnace, as a result of the splashing of the layer of slag consequent upon agitation thereof. 'I'his solidified layer of litharge is found to protect from corrosion the refractories forming the walls and the roof and to reduce the dissipation of heat from the furnace.

The violent agitation of the molten bodies necessary to produce homogeneity is such as to prevent the existence of separable layers of slag and bullion adjacent to the air jets and in order that the slag may be eectively separated at. the discharge orifice therefor the air jets are so disposed as to provide sclently quiescent conditions adjacent thereto.

It will be underst that, by suitably regulating the introduction of air through the submerged jets, the use of extraneous heating may be reduced to any desired extent and that consequently this aspect of the invention is not connned to the elimination of extraneous heating means but to their being so reduced that the fuel consumption per ton of bullion treated is substantially lower than the best results obtained in previous softening practice.

It will be clear that, when the process is so operated as to substantially dispense with extraneous heating, a larger proportion of dross is formed than would otherwise be the'case, but, as the correspondingly larger amount of hard lead subsequently produced from the antimony dross may be delivered direct to the zinc refining furnace instead of being returned to the softening furnace (as in ordinaryreilning practice), and then being subsequently subjected to the ordinary desilverizing process, this larger volume of dross does not occasion any disadvantage.

In order to render it practicable to deliver direct to the zinc renning furnace the antimony dross or the antimony slag or hard lead produced from the antimony dross, it is necessary that such antimony dross should be low in silver and copper.

In this connection, it is pointed out that the said antimony dross is of low grade in silver if the slag layer in the softening furnace is sumciently thick (say 2 inches or more) to enable it to be readily removed from the softening furnace without entrainment of bullion.

Also the copper grade of the hard lead can be kept suillciently low by operating the previous copper dressing treatment so vthat 'a maximum recovery of copper is obtained. This is not necessary in ordinary lead refining procedure (in which all of the bullionv passing to the zinc renning furnace has been subjected to the usual desilverizing process) because any undesirable amounts of copper remaining in the bullion are removed by the desilverizing treatment.

An important advantage'of the continuous softening process, when operated under such conditions that extraneous heating is substantially dispensed with is that the maintenance costs of the furnace are' considerably reduced.

A still further important 'advantage of the continuous softening procss, when operated under such conditions, is that a considerably smaller furnace may be used for a given output of softened bullion as compared'with the batch treatment generally used. For example, a furnace having a holding capacity of about l5 tons of metal may, when used in accordance with the present invention, soften as much lead in a given time as a batch softening furnace having a holding capacity of 300 tons.

In addition, it has been found that loss of metal by volatilization is also reduced by operating in accordance with the present invention.

Eample.-Smelter lead'produced from Broken Hill ores was continuously delivered at a temperature of about 400 C. and at the rate of 18 tons per hour, through orifice I0 to a reverberatory furnace (shown in Figures l and 2). The furnace was 5 feet wide and 15 feet long internally,

and softened lead and slag were continuously discharged from separate notches outlet openings i l and i2 respectively in opposite ends of the furnace.

A dam or e it extending below the slag layer adjacent to the notch or opening i i served to prevent the dischargeof slag throughsaid notch or opening.

The average depth of bullion in the furnace was approximately 8 inches and the thickness of the slag layer about two inches.

The temperature of the 'metal bath was maintained at about 780 C. to l800" C. and the whole of the heat necessary to raise the temperature of the inilowing bullion and also to make good the losses from the furnace was obtained from the oxidation of the lead and of the antimony and arsenic therein so that no extraneous heating means were used.v

For this purpose the bath of metal was subjected to intense agitation by means of air at a pressure vof `lbs. per sq. inch which was delivered by means of three air pipes Il extending vertically downwards through the top of the furnace and into the said bath. Each of the air pipes was provided at its lower end with eight discharge openingsof diameter.

'lhis intense agitation of the bath of metal by the air iets 4served to maintain substantially homogeneous conditions in the bullion and in the slag.

`The inflowing unsoftened bullion assayed:-

Copper per cent 0.004 y Arsenic per cent 0.19 Antimony.- per cent 0.65 Silver ounces per ton 47.2 G'old ounce per ton 0.10

whilst the outilowing softened bullion assayed:-

Copper per'cent 0.004 Arsenic less than per cent 0.0005 Antimony per cent 0.01 Silver ounces per ton 47.7 Gold... ounce per ton 0.10

The weight of slag formed was about 280 lbs. pe ton of bullion delivered to the furnace and it Antimony. ----per cent 5.0`

Arsenic per cent 1.5 Silver ounce per ton 0.2

n' u to'be noted that, whilst 'it is preferred to carry out the continuous softening process m a.

Aco

` of said homogeneous conditions.

Continuous zinc refining process In the practice of my improved process of zinc refining as applied tothe treatment of argentiferous smelter lead, desilverized lead containing zinc 4may be Vcaused to flow continuously into a reverberatory refining furnace, whilst refined lead low in zinc is continuously discharged from a different portion thereof.

The furnace may be itted with oil burners or other means for maintaininga desired temperature therein, and the usual means may be provided for maintaining and controlling an oxidizing atmosphere in the furnace.

Antimony and/or arsenic, preferably in the form of antimony slag (of low grade in copper and silver) or hard lead, produced from antimony dross, are also supplied to the furnace either continuously or intermittently and either separately from, xor in conjunction with, the desilverized lead supplied to the furnace.

One effect of this addition of antimony and/or arsenic is to reduce the melting point of the slags which are formed in the furnace by the oxidation of the zinc and antimony contents of the bullion, and also some of the lead, with the result that, at ordinary operating temperatures (about 800 C.) the slag exists in a liquid condition above the bullion passing through the furnace.

The -bullion and slag layers are subjected to intense agitation as by means of air jets submerged vin the bullion, in order that substantially 'uniform conditions of composition and temperature will be maintained in the slag and in the bullion which latter is thus uniformly low in antimony andzinc which condition is favorable to rapid oxidation and consequently is favorable to rapid refining of the incoming bullion. l

It has been found also that the presence of substantial amounts of antimony and/or arsenic in the slag promotes the oxidation process, so

that, under the conditions set up by the airjets, oxidation proceeds rapidly. r Y

The refined lead is discharged continuously from the furnace through an orifice which is disposed below the surface of separation of the slag and bullion layers, as, in the softening furnace shown in Figures 1 and 2, said discharge orifice being ordinarily arranged at the opposte end of the furnace to the `feed vopening thereof.

The liquid slag containing oxides of lead zinc and antimony-is caused to fiow either -continuously or4 intermittently throughan opening or notch disposed at such a distance above the level of the bullion as to allow a layer of slag of sufficient thickness to be maintained in the furnace.

In order to effectively separate the slag from the bullion in the manner described, it is. preferred to operate under such conditions that a relatively thick layer of slag-say of the order of about 2 to 4"-is formed and maintained above the bullion.

As previously stated, desilverized lead bullion,

in addition to containing zinc in the approximate proportions above set forth (i. e. 0.55%) usually contains a small amount of antimony, and it is important that this antimony content of the lead should be reduced to negligible proportions by 5 the zinc refining operation.

However, it has been found that, with the present invention, in which antimony is separately added to the zinc refining furnace or to the lead to be subjected to treatment therein, it is possible to readily produce refined or market lead having an antimony content which isy as low as, or is lower than, the antimony content of ,lead which is refined without such additions of antimony being made. l5

It will be clear, therefore, that, whilst one of the objects of the usual zincreiining process is to reduce the antimony content of the lead bullion, this object is effectively attained by the present invention in which antimony is deliberately added for the purpose of facilitating the zinc refining operation.

EampZe.-Desilverized lead bullion produced from Broken Hill ores and containing .55% zinc and .01% antimony and a trace of arsenic, was continuously delivered to the refining furnace at the rate of 20 tons per hour.

The average depth of bullion in the refining furnace (which was similar Vto the softening furnace shown in Figures 1 and 2) was about 18"-30 whilstthe internal plan dimensions of the furnace were 5'0 x 150".

A temperature of about 800 C. was maintained in the furnacewith the aid of an oil burner and refined lead continuously discharged therefrom assayed .00023% zinc and .00l7% antimony.

Antimony slag averaging 16% antimony and 5% arsenic was continuously supplied to the furnace at the rate of 0.25 ton per hour.

The amount of antimony separately supplied to the furnace was thus equal to 0.2% of the lead treated whilst the total amount of antimony passing through the furnace was of the lead treated.

Likewise, the amount of arsenic separately supplied to the furnace was equal to. 0.6% of the 4 lead treated. 50

The effect of the addition of these quantities of antimony and arsenic was to lower the melting point of the zinc dross, thus making it possible to produce it as a liquid slag without operating at temperatures in excess of the temperatures at which the ordinary batch treatment is usually carried out.

'I'he liquid slag was allowed' to accumulate in the furnace until a layer of about 3 in thickness was formed after which the excess was d's- 60 charged continuously through a notch.

In order to agitate the bullion and slag, air at a pressureof 80 lbs. per square inch was supplied to the furnace by means of eight submerged jets having orifices 1/4" in diameter. 65

Whilst the beneficial effects of adding antimony may be obtained by adding that metal over a fairly wide range of proportions, it will be clear that, as the chief objective in making the additions is to depress the melting point of the slag to a convenient operating temperature, the above quoted example, in which a total of about 0.21% antimony was present in the furnace, constitutes a general guide as to the amount of antimony suitable for the purpose.

lili

` gentiferous smelter lead is desilverized with the aid of zinc, the said process is equally applicable to the refining of zinciferous lead obtained from other sources.

As above stated, it is preferred to add antimony and/or arsenic to the refining furnace in order to depress the melting point of the slags formed therein, but it is to be understood that this invention includes the continuous refining of zincifcrous lead without such additions of antimony and/or arsenic being made.

When operating without the addition of such reagents, it is necessary to raise the operating' temperature to obtain the slag in the liquid condition, but this procedure increases the cost of operation both in fuel and in maintenance.

lt is also possible to operate the continuous nino refining process under such conditions of temperature that the dross is removed either continuously or intermittentlysin a solid condition.

Combined refining operations As above stated, an important advantage accruing from the combined use of the continuous softening and zinc refining processes resides in delivering direct to the zinc refining furnace the antimony dross (from the softening furnace) or the antimony slag and/or hard lead produced therefrom.

It has previously been explained that the hard lead produced from antimony dross obtained in accordance with this invention, is of low content in silver and copper, and also that it is advantageous for the antimony and arsenic contents thereof to be delivered direct to thezinc refining furnace.

Consequently, it is unnecessary to return the hard lead to the softening furnace, as is normally done, firstly, for the recovery of the antimony and arsenic contents and in a subsequent desilverization process for the recovery of the silver content. v

As this hard lead, produced under ordinary softening practice at the Port Pirie (South Australia) Refinery, amounts to about of the bullion treated, a considerableeconomy is effected by delivering it direct to the zinc refining furnace and so obviating the necessity of returning such hard lead to the softening furnace, and subsequently to the ordinary desilverizing process.

Furthermore, when the cdtinuous softening process is operated under such conditions as toobviate the use of any substantial degree of extraneous heating, the production of hard lead may amount to of the bullion treated in the softening furnace, thus increasing the amount of lead which by-passes the desilverizin'g process.

. ing point than would otherwise be formed.

ly or intermittently, direct to the zinc refining furnace.

1. The process of rening lead comprising causing lead bullion containing readily oxidizable 5 alloying metals, to ow continuously into a treating chamber, and continuously discharging lead low in such alloying metal from the chamber, said bullion, during its passage through the chamber, being subjected to oxidation by air and to 10 agitation by means of submerged jets whereby. oxides of lead and of said alloying metals separate as a liquid slag which exists above the bullion and is progressively discharged therefrom, characterized in that the agitation ls sulciently intense to maintain uniform conditions of temperature and of composition in the bullion and the heat of formation of the metallic oxides produced is substantially suicient in itself to maintain the requisite reaction temperature within the chamber.

.2. The process of refining lead according to claim 1 wherein the temperature of the inflowing lead is substantially lower than the reaction temperature maintained in the chamber.

3. A process of rening zinciferous lead bullion 4comprising continuously delivering bullion to a chamber, continuously discharging refined lead from the chamber and maintaining such conditions of temperature and oxidation therein that oxides of zinc and lead are formed and exist above the bullion as a liquid slag, said slag being progressively discharged from the furnace, characterized in that a reagent selected from the group consisting of antimony arsenic, compounds of antimony and arsenic, antimony dross and hard lead and antimony slag produced from antimony dross is supplied to the lead treated in the chamber, to produce a slag of lower melt- 4. A process of refining zinciferous lead bullion comprising continuously delivering bullion to a chamber, continuously discharging refined lead from the chamber, maintaining such conditions oftemperature and oxidation in the chamber that oxides of zinc and lead are formed and exist above the bullion as a liquid slag, discharging slag from the chamber and supplying direct to the chamber or to the lead to be treated therein, a reagent adapted to lower the melting point 5- of the slag formed, said reagent being selected from the group consisting of antimony and arsenic and compounds containing same, and characterized in that the bullion within the chamber is subjected to such intense agitation that substantially uniform conditions of temperature and composition exist therein.

5. A process for reiining zinciferous `smelter lead according to claim 4 wherein antimony is 60 supplied to the chamber at a rate approximately equal to from .2% to .4% of the buillion supplied during the same period.

6. A process for producing rened lead from smelter buillion comprising continuously delivering the bullion to a softening furnace in which the requisite conditions of temperature and oxidation are maintained, and continuously discharging softened bullion therefrom, subjecting the softened bullion to a desilverizing treatment, supplying desilverized bullion continuously to 'a zinc refining furnace, discharging liquid antimony dross low in copper and silver from the sftening furnace, supplying said antimony dross to the zinc rening furnace iniwhich the requisite 1g l conditions of temperature and oxidation are maintained, continuously discharging refined lead from the zinc refining furnace, and discharging liquid slag therefrom.

' 7. A process for producing refined lead from smelter buillion comprising continuously delivering the bullion to a softening furnace in which the requisite conditions of temperature and oxidation .are maintained, and continuously discharging softened bullion therefrom, subjecting the softened bullion to a desilverizing' treatment, supplying desilverized bullion continuously to a zinc refining furnace, discharging liquid antimony dross low in copper and silver from the softening furnace, reducing the antimony dross to produce antimony slag and hard lead, supplying the hard lead and antimony slag so produced to the zinc rening furnace in which the requisite conditions of temperature and oxidation are maintained continuously discharging rened lead 'from the zinc refining furnace and discharging liquid slag therefrom.

8. The process of refining lead which comprises continuously passing into a treating chamber molten lead bullion containing readily oxidizable alloying metal, continuously discharging -from said chamber molten lead low in such alloying metal, maintaining an oxidizing atmosphere and suitable temperature conditions within the chamber and subjecting the bullion Within the chamber to agitation of such intensity that substantially uniform conditions of temperature and of composition exist throughout the bullion bath whereby oxides of lead and of said alloying metal separate as a liquid slag which exists above the bullion and progressively discharging said slag from the chamber.

9. The process of rening lead which consists in vcontinuously passing into a treating chamber molten lead bullion containing readily oxidizable alloying metal, continuously discharging from the chamber lead low` in such alloying metal, subjecting the bullion within the chamber to intense agitation and to oxidation by air under suitable conditions of temperature whereby oxides of lead and of said alloying metal separate as a liquid slag which exists above the bullion, said agitation being of such intensity as to cause substantially uniform conditions of temperature and of composition toI exist throughout the bullion bath, and progressively 4discharging said liquid slag from the chamber.

10. The process of rening lead Which consists in continuously passing molten lead bullions containing readily oxidizable alloying metal into a treating chamber, continuously discharging from said chamber molten lead low in such alloying metal, maintaining an oxidizing atmosphere and the requisite temperature conditions Within the chamber and subjecting the bullion within the chamber to agitation by jets of gas, said agita.- tion beingof such intensity that substantially uniform conditions of temperature and of composition exist throughout the bullion bath whereby oxides of lead and of said alloying metal -separate as a liquid slag which exists above the bullion, and progressively discharging said slag from the chamber.

11. The process of refining lead Which'consists in continuously passing molten lead bullion containing readily oxidizable alloying metal intoI a treating chamber, continuously discharging from said chamber molten lead low in such alloying metal, maintaining the requisite temperature conditions within the chamber and subjecting the bullion Within the chamber to agitation by submerged jets of air, said agitation being of such intensity that substantially uniform conditions of temperature and of composition exist throughout the bullion bath whereby oxides of lead and of said alloying metal separate as a liquid slag which exists above the bullion, and progressively discharging said slag from the chamber.

12. The process of refining lead according to claim 9 wherein a layer of liquid slag of at least two inches in thickness is maintained in the chamber above the bullion.

13. Ihe process of refining lead which comprises continuously passing into a treating chamber molten lead bullion containing readily oxidizable alloying metal, continuously discharging from said chamber molten lead low in such alloying metal, maintaining an oxidizing atmosphere .and the requisite temperature conditions within Y the chamber and subjecting the bullion within.

the chamber to agitation by submerged jets of air, said agitation being of such intensity that substantially uniform conditions of temperature and of compositionexist throughout the bullion bath and that the heat of formation of the metallic oxides produced is substantially suicient in itself to maintain the requisite reaction temperature within the chamber, said metallic oxides' separating as a liquid slag exists above the bullion, and progressively discharging said slag from the chamber.

14. The process of rening lead which consists in continuously passing into a treating chamber molten lead bullion containing readily oxidizable alloying metal, continuously discharging from the chamber lead low in such alloying metal, subjecting the bullion Within the chamber t intense agitation and to oxidation by air under suitable conditions of temperature whereby oxides of lead and of said alloying metal separate as a liquid slag which exists above the bullion, and progressively discharging said liquid slag from the chamber, said agitation being of such intensity as to cause substantially uniform conditions of temperature and of composition to exist throughout the bullion bath and the heat of formation of the metallic oxides produced to be substantially sucient in itself to maintain the requisite 60 reaction temperature Within the chamber.

GEORGE KENNETH WILLIAMS. 

